I just read an article "Secrets of the Huston Warehouse" where a group of Bench Rest Shooters got to gether trying for the one hole group inside a 300 yard warehouse.
From the article primers didn't make much of a difference.
However, saying that, I found in some cases they do. I have a Ruger #1 in 204 Ruger. Wife bought it for me when it first came out.
I started with the accuracy load listed by Sierra. I was using fed match primers and CCI Bench rest primers.
I didn't get any where near the accuracy I wanted nor the velocity Sierra listed.
I switched nothing but primers, going to CCI Standard SR primers. I found the accuracy I wanted and it dern near equaled the velocity Sierra listed.
Personally I'd go buy a box (100) of each and see what worked in your rifle and you load.
Over the years I've found what works for one, may not work for others, what works in some rifles may not work in others.
So as to the question, "which is the best primer"? Got Me. Heaven only knows.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071